Carburetor for two-cycle engine

ABSTRACT

An interlocking lever having first and second cam faces is mounted on a throttle valve stem, and a throttle valve is arbitrarily opened to perform start-up in a state in which the first cam face makes contact with the choke valve lever and the interlocking lever is stopped during low-temperature start-up with the choke valve closed. After the choke valve has been returned to the fully open position, the throttle valve alone is opened with a small degree of opening to perform low-load operation; and in the mid- and high-load region, the interlocking lever integrally turns with the throttle valve, the second cam face pushes the air valve lever, and the throttle valve and air valve are caused to open and close proportionally.

FIELD OF THE INVENTION

The present invention relates to carburetor for supplying fuel to atwo-stroke engine in which scavenging air is introduced to the fuelchamber prior to an air/fuel mixture.

BACKGROUND OF THE INVENTION

Widely known are two-stroke engines in which scavenging air isintroduced to the combustion chamber during the downward stroke of thepiston, and an air/fuel mixture is introduced to the combustion chamberafter exhausting combustion gas. These methods of introduction includefeeding scavenging air to a scavenging channel connected to thecrankcase and the fuel chamber and also feeding an air/fuel mixture tothe crankcase. Alternatively, scavenger air is introduced to the fuelchamber and an air/fuel mixture is introduced to the crankcase tointroduce scavenging air to the fuel chamber in the order describedabove.

The flow rate of scavenging air and the air/fuel mixture must be madeproportional in order to prevent incomplete combustion, stabilize engineoperation, and so forth. An air valve is therefore provided to the airchannel for supplying scavenging air to the engine. The air valve isoperated in coordination with the throttle valve of the carburetor. Inthis case, when the valves are butterfly throttle valves, the air valveis also a butterfly valve, and it is common to link these with awidely-known link mechanism, as cited in Japanese Patent ApplicationLaid-open Nos. 9-125966 and 2000-314350 and International PatentApplication WO01/51782A1, for example.

When the carburetor is provided with a choke valve, start-up isadequately performed by causing high negative pressure to act on themain nozzle in a condition in which the choke valve is closed and thethrottle valve is opened slightly at low temperatures. At this time, theair valve must be closed. When a link mechanism (refer to JapanesePatent Application Laid-open No. 2000-314350) configured so that the airvalve is opened after the throttle valve has been opened to a certaindegree is used in order to achieve this goal or to prevent the air/fuelmixture from becoming thin during low loads, a drawback tends to arisein that the operator cannot determine the point in time at which the airvalve begins to open, so the throttle valve is allowed to open until theair valve opens, making it impossible to obtain a high density air/fuelmixture required for start-up at low temperatures.

As a countermeasure, it is possible to consider interlocking a throttlevalve and a choke valve with a link mechanism, and opening the throttlevalve in a range in which the air valve does not open when the chokevalve is closed. However, there is a drawback when this countermeasureis adopted in that two mutually independent link mechanisms are used,the configuration becomes complex, the number of components greatlyincreases, and a fairly large installation space must be set aside whenmounting the structure on an engine.

SUMMARY OF THE INVENTION

The present invention was developed to solve the above-describeddrawback of not having a simple interlocking mechanism in which thethrottle valve can open without causing the air valve to open when thechoke valve is closed in a carburetor for a two-stroke engine in whichthe air valve is interlocked with the throttle valve. Accordingly, anobject of the present invention is to provide a carburetor for atwo-stroke engine that has an interlocking mechanism in which properopening and closing action can be carried out with a simpleconfiguration and a small number of components.

The present invention is configured as follows in order to solve theabove-described problems in a carburetor for a two-stroke engine havingan air intake passage that accommodates a throttle valve and a chokevalve and feeds an air/fuel mixture to the engine, and an air channelthat accommodates an air valve and feeds scavenger air to the engine. Inone embodiment according to the present invention, the throttle valve isconfigured so that an interlocking lever having a first and second camsurface is independently rotatably mounted on the throttle valve with orwithout following the opening and closing action of the throttle valve.The choke valve is configured so that a valve-opening spring is fixedlymounted on the choke valve stem to provide a valve-opening force forurging the choke valve and the choke valve lever in contact with thefirst cam face. The air valve is configured so that a valve-closingspring is fixedly mounted on the air valve stem to provide avalve-closing force for urging the air valve and the air valve lever incontact with the second cam face. The choke valve lever is placed in theregion beyond the turning of the interlocking lever in a state in whichthe choke valve is open, but is brought into contact with the first camface, restrains the interlocking lever at a position in which the secondcam face does not make contact with the air valve lever, and brings theair valve into a closed state when the choke valve is in a closed state.Also, the interlocking lever is configured so that when the restraint bythe choke valve lever is released, the second cam face makes contactwith the air valve lever at or above a certain degree of opening of thethrottle valve to cause the air valve to open in accordance with theopening of the throttle valve.

More particularly, the interlocking lever is set in a position in whichthe air valve is held in a closed state by the choke valve lever whenthe choke valve is closed, and the throttle valve alone is allowed to befully open. Also, the first cam face is formed so that the choke valvelever causes the interlocking lever to stop at a position at which thesecond cam face does not make contact with the air valve lever betweenthe fully closed position of the choke valve and a positioncorresponding to a certain degree of opening.

When starting up an engine at low temperatures with a carburetor withthe above-described configuration, normally the choke valve is caused toclose in a state in which the throttle valve and the air valve areclosed and the choke valve is open. Next, when the throttle valve isopened in order to secure start-up fuel, the interlocking lever thatturns with the opening of the valve is stopped when the first cam facemakes contact with the choke valve lever, the throttle valve alone turnsthereafter and is opened to the fully open position, and the air valveis held in the closed position. The operator can thereby adopt anoperation method whereby the throttle valve is fully opened to performcranking in order to ensure start-up at low temperatures.

When the engine has completed firing up, the throttle valve is normallyreturned to the idle position, and the choke valve is operated so as togradually open or to fully open in a single action. Usual actions arecarried out in the sense that after warm-up is completed theinterlocking lever integrally turns with the throttle valve withoutinterference from the choke valve lever, the throttle valve is openwhile the air valve remains closed in the low-load region, and the airvalve opens in coordination with the throttle valve in the mid- andhigh-load regions.

It is preferable to properly carry out the above-described action in aconfiguration in which the throttle valve stem fixedly supports athrottle valve lever and rotatably supports an interlocking lever, and areturn spring for urging the throttle valve with a valve-closing forceis provided so as to be latched at both ends to the throttle valve leverand the interlocking lever.

In another embodiment according to the present invention, the throttlevalve is configured so that a return spring is fixedly mounted to thethrottle valve stem to provide valve-closing force for urging thethrottle valve and the interlocking lever having a contact face and acam face. The choke valve is configures so that a valve-opening springis fixedly mounted on the choke valve stem to provide a valve-openingforce for urging the choke valve and the choke valve lever in contactwith the contact face of the interlocking lever. The air valve isconfigured so that a valve-closing spring is fixedly mounted on the airvalve stem to provide a valve-closing force for urging the air valve andthe air valve lever in contact with the cam face. The choke valve leveris placed in the region beyond the turning of the interlocking lever ina state in which the choke valve is open, but is brought into contactwith the contact face, limits the rotation of the interlocking lever ina position at or below the position in which the cam is kept in contactwith the air valve lever, and keeps the air valve in a closed state whenthe choke valve is in a closed state. Also, the interlocking lever isconfigured so that when the limitation of the choke valve lever isreleased, the cam face makes contact with the air valve lever at orabove a certain degree of opening of the throttle valve to cause the airvalve to open in accordance with the opening of the throttle valve.

When an engine is started up at low temperatures with a carburetorconfigured as described above, the air valve is kept in the closedposition and the throttle valve is opened to within a certain degree ifthe choke valve is closed. Because of this, the throttle valve cannot befully opened to perform cranking, but start-up at low temperatures canbe reliably carried out with a normal operational method in which thethrottle valve is slightly opened to secure start-up fuel. The same asthat described above is employed for opening the choke valve, thenopening the throttle valve while keeping the air valve closed in thelow-load region, and interlocking the throttle valve and opening the airvalve in the mid- or high-load region.

According to the present invention, a simple interlocking mechanism thathas a minimum number of components that is provided with an interlockinglever, a choke valve lever, an air valve lever, and springs mounted onthese levers can be used to perform start-up at low temperatures byclosing the choke valve and the air valve and suitably opening thethrottle valve, to open the throttle valve with the air valve remainingclosed in a low-load region, and to open the air valve in interlockedfashion with the throttle valve in the mid- or high-load region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional schematic diagram of the carburetorto which the present invention is applied;

FIG. 2 is a front view showing an embodiment of the present invention;

FIG. 3 is an enlarged partial diagram viewed in the direction of arrow Ain FIG. 2;

FIG. 4 is an operation schematic diagram of the embodiment shown in FIG.2;

FIG. 5 is a front view showing another embodiment of the presentinvention; and

FIG. 6 is an operation schematic diagram of the embodiment shown in FIG.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below with referenceto the drawings. FIG. 1 is a longitudinal sectional schematic diagram ofthe carburetor to which the present invention is applied, wherein a body9 is overlaid and affixed to the upper face of a carburetor 1. Thecarburetor 1 has an air intake passage 2 that extends in the lateraldirection for feeding an air/fuel mixture to the engine, and a diaphragmtype constant fuel chamber 8 formed on the lower face. The air intakepassage 2 has, in order from the inlet to the outlet, a choke valve 3, aventuri 5, and a throttle valve 6. The fuel in the constant fuel chamber8 passes through the main fuel channel leading to the main nozzle (notdepicted) open to the venturi 5, and through the low-speed fuel channelleading to the idle and slow ports (not depicted) open to the rear ofthe throttle valve 6, to be delivered to the air intake passage 2.

The body 9 has an air channel 10 that extends in the lateral directionfor feeding scavenger air to the engine, and an air valve 11 is disposedin the air channel 10. The choke valve 3, throttle valve 6, and airvalve 11 are all butterfly valves, and the choke valve stem 4, throttlevalve stem 7, and air valve stem 12 of these protrude to the side faceon the same side of the carburetor 1 and body 9.

Referring to FIGS. 2 and 3, a choke valve lever 15, a throttle valvelever 17, and an air valve lever 18 are fixedly mounted to theprotruding ends of the choke valve stem 4, throttle valve stem 7, andair valve stem 12. The choke valve 3 is urged in the valve openingdirection by a force produced by a valve opening spring 16 composed of atorsion spring which is mounted around the choke valve stem 4 and bothends of which are latched to the carburetor main body 1 and the chokevalve lever 15. The air valve 11 is urged in the valve closing directionby a force produced by a valve closing spring 19 composed of a torsionspring which is mounted around the air valve stem 12 and both ends ofwhich are latched to the body 9 and the air valve lever 18.

An interlocking lever 20 is rotatably mounted to the protruding endportion of the throttle valve stem 7. This interlocking lever 20 has aboss 21 fitted to the throttle valve stem 7 at the base end portion, anda protruding stopper 22 that is in contact with the receiving edge 17 aprovided on the throttle lever 17. A first cam face 23 and a second camface 24 are formed adjacent to each other in a stepwise manner along theend edge that faces the choke valve lever 15 and the air valve lever 18.The choke valve lever 15 and the first cam face 23 are disposed in thesame plane and turn in this plane; the air valve lever 18 and the secondcam face 24 are disposed in another same plane and turn in this plane.The choke valve lever 15 and the air valve lever 18 turn without oneinterfering with the other. The installation position of the air valve11 can be arbitrarily moved with respect to the throttle valve 6 andchoke valve 3.

Furthermore, the throttle valve 6 is urged in the valve closingdirection by a force produced by a return spring 25 composed of atorsion spring which is mounted around the throttle valve stem 7 andboth ends of which are latched to the throttle valve lever 17 and theinterlocking lever 20.

An accelerator lever is mounted on the opposite end of the throttlevalve stem 7, and the throttle valve 6 is opened when the operatorapplies an accelerator action to the accelerator lever. Also, the chokevalve 3 is configured to close when the operator applies a choke actionto the choke valve lever 15. FIGS. 1 and 2 show a situation in which thechoke valve 3 is set in the fully open position, the throttle valve 6 isset in the idle position, the air valve 11 is set in the fully closedposition, and the engine is stopped or idling. The interlocking lever 20is stopped by the return spring 25 pressing the stopper 22 against thereceiving edge 17 a of the throttle lever 17 in the idle position,whereby the choke valve lever 15 and the first cam face 23 are separatedfrom each other, as are the air valve lever 18 and the second cam face24.

When the choke valve 3 is fully closed in order to start the engine atlow temperatures, the choke valve lever 15 is positioned as shown inFIG. 4(A). When the throttle valve 6 is in the idle position, the firstcam face 23 is separated from the choke valve lever 15, but when thethrottle valve 6 is opened in order to ensure start-up fuel, the firstcam face 23 makes contact with the choke valve lever 15 the moment thethrottle valve is slightly opened. The choke valve lever 15 thereafterserves as a stopper, and the throttle valve 6 is opened with theinterlocking lever 20 left in a stopped condition. Because the air valve11 is stopped in a position in which the second cam face 24 is separatedfrom the air valve lever 18, the fully closed position is maintained.FIG. 4(A) shows the state in which the throttle valve 6 is fully open,and this configuration has advantages in that start-up can be performedwith the throttle valve 6 at any degree of opening between a positionslightly open from the idling position to a fully open position, and thedegree of freedom in throttle valve operation during start-up at lowtemperatures is the largest.

When the engine has completed firing up, the throttle valve 6 isnormally returned to the idle position, and the choke valve 3 isgradually opened or is fully opened in a single action. In this case,when the choke valve 3 is set to a slightly open position and thethrottle valve 6 is opened from the idle position, the interlockinglever 20 stops at a position in which the first cam face 23 is incontact with the choke valve lever 15. For this reason, the throttlevalve 6 can be arbitrarily opened while keeping the air valve 11 in theclosed position to perform stable warm-up operation. An unloaderfunction can furthermore be imparted by opening and holding the chokevalve 3 within a region in which the degree of opening is such that theinterlocking lever 20 is stopped in a range in which the second cam face24 does not make contact with the air valve lever 18. FIG. 4(B) showsone of such states, and the throttle valve 6 is opened slightly furtherthan in the idle position.

In the present embodiment, in order to properly perform theabove-described operation, the first cam face 23 is formed so that thechoke valve lever 15 stops the interlocking lever 20 at a position atwhich the second cam face 24 does not make contact with the air valvelever 18 between the fully closed position of the choke valve 3 andposition corresponding to a certain degree of opening.

The choke valve 3 is fully opened when warm-up is completed, and thereturn spring 25 causes the interlocking lever 20 to integrally turnwith the throttle valve 6. In a low-load region in which the degree ofopening of the throttle valve 6 is small, the air valve 11 is not causedto open by the second cam face 24 coming into contact with the air valvelever 18, so situations can be prevented in which an air/fuel mixturealone from the air intake passage 2 is fed to the engine, the air/fuelmixture created with fuel from primarily the low-speed system is madethinner, and the engine performs poorly. When the throttle valve 6 isopened to a considerable extent, the second cam face 24 causes the airvalve lever 18 to turn and open the air valve 11. These states passthrough a mid-load region shown in the half-open state in FIG. 4(C) andarrive at a high-load region shown in the fully open state in FIG. 4(D).

The degrees of opening of the throttle valve 6 and the air valve 11 aresubstantially proportional, and the flow rates of the air/fuel mixtureand the scavenger air fed to the engine are therefore substantiallyproportional, but the ratio at which the flow rate of the scavenger airvaries with respect to the air/fuel mixture can be arbitrarily set bythe shape of the second cam face 24.

FIG. 5 shows another embodiment of the present invention in which achoke valve lever 35, an interlocking lever 40, and an air valve lever38 are fixedly mounted to the protruding ends of the choke valve stem 4,throttle valve stem 7, and air valve stem 12. The choke valve 3 is urgedin the valve opening direction by a force produced by the same valveopening spring 36 as the above-described embodiment. The throttle valve6 is urged in the valve closing direction by a force produced by areturn spring 45 composed of a torsion spring which is mounted aroundthe throttle valve stem 7 and both ends of which are latched to thecarburetor main body 1 and the interlocking lever 40. The air valve 11is urged in the valve closing direction by a force produced by the samevalve closing spring 39 as the above-described embodiment

The interlocking lever 40 has a contact face 43 and a cam face 44 whichare formed adjacent to each other in a stepwise manner along the endedge that faces the choke valve lever 35 and the air valve lever 38. Thechoke valve lever 35 and the contact face 43 are disposed in the sameplane and turn in this plane. The air valve lever 38 and the cam face 44are disposed in another same plane and turn in this plane.

FIG. 5 shows a situation in which the choke valve 3 is set in the fullyopen position, the throttle valve 6 is set in the idle position, the airvalve 11 is set in the fully closed position, the engine is stopped oridling, and the choke valve lever 35 and the contact face 43 areseparated from each other, as are the air valve lever 38 and the camface 44.

When the choke valve 3 is fully closed in order to start the engine atlow temperatures, the choke valve lever 35 is positioned as shown inFIG. 6(A). When the throttle valve 6 is in the idle position, thecontact face 43 is separated from the choke valve lever 35. When thethrottle valve 6 is opened in order to ensure start-up fuel, the contactface 43 makes contact with the choke valve lever 35 when the throttlevalve is slightly open, and the throttle valve 6 is not opened further.On the other hand, the cam face 44 is separated from the air valve lever38, and the air valve 11 is kept in the fully closed position. FIG. 6(A)shows the state at this time, and start-up can be performed with thethrottle valve 6 at any degree of opening between the idling positionand the position shown in the diagram, but start-up is commonlyperformed at the position corresponding to the degree of opening shownin the diagram. According to the present embodiment, the degree offreedom in throttle valve operation during low-temperature start-up issmall, but an operator who adopts an operating method in which theengine is started with a slightly opened throttle valve 6 can beprovided with a sense of confidence that the opening can always be keptconstant.

When the engine has completed firing up and the choke valve 3 is opened,the choke valve lever 35 disengages from the contact face 43 the momentthe valve is slightly opened from the completely closed state. The chokevalve 3 thereafter gradually or abruptly opens. Unrelated to thisaction, the throttle valve 6 can be opened and closed, and warm-upoperation performed, in a range in which the cam face 44 is not allowedcontact with the air valve lever 38. Therefore, in the presentembodiment, the contact face 43 is formed so that contact is made withthe choke valve lever 35 between the fully closed position of the chokevalve 3 and a position slightly open from this state, and contact is notmade at positions opened to a greater extent.

After the choke valve 3 has returned to the fully opened position whenwarm-up is completed, the cam face 44 keeps the air valve in the closedposition without making contact with the air valve lever 38 in thelow-load region in which the throttle valve 6 has a small degree ofopening, but as the throttle valve 6 is opened to a considerable extent,the cam face 44 of the integrally turning interlocking lever 40 causesthe air valve lever 38 to turn and open the air valve 11. These statespass through the mid-load region shown in the half-open state in FIG.6(B) and arrive at the high-load region shown in the fully open state inFIG. 6(C). The relationship between degrees of opening of the throttlevalve 6 and the air valve 11, in other words, the ratio at which theflow rate of the scavenger air varies with respect to the air/fuelmixture in the present embodiment, can be arbitrarily set by the shapeof the cam face 44 in the same manner as the above-described embodiment.

1. A carburetor for a two-stroke engine having an air intake passagethat accommodates a throttle valve and a choke valve and feeds anair/fuel mixture to the engine, and an air channel that accommodates anair valve and feeds scavenger air to the engine, comprising: aninterlocking lever that has a first and second cam surface and isrotatably mounted on a throttle valve stem and selectively restrainablefrom following the opening and closing action of the throttle valve; avalve-opening spring fixedly mounted on the choke valve stem to providea valve-opening force for urging a choke valve and the choke valve leverin contact with the first cam face; and a valve-closing spring fixedlymounted on an air valve stem to provide a valve-closing force for urgingthe air valve and an air valve lever in contact with the second camface, wherein a choke valve lever is placed in the region beyond theturning of the interlocking lever in a state in which the choke valve isopen, but is brought into contact with the first cam face and restrainsthe interlocking lever at a position in which the second cam face doesnot make contact with the air valve lever, and wherein the valve-closingspring brings the air valve into a closed state when the choke valve isin a closed state, and wherein the interlocking lever is configured sothat when the restraint by the choke valve lever is released, the secondcam face makes contact with the air valve lever at or above a certaindegree of opening of the throttle valve to open the air valve.
 2. Thecarburetor for a two-stroke engine according to claim 1, wherein theinterlocking lever is set in a position in which the air valve is heldin a closed state by the choke valve lever when the choke valve isclosed, and the throttle valve alone is allowed to be fully open.
 3. Thecarburetor for a two-stroke engine according to claim 1, wherein thefirst cam face is formed so that the choke valve lever causes theinterlocking lever to stop at a position at which the second cam facedoes not make contact with the air valve lever between the fully closedposition of the choke valve and a position corresponding to a certaindegree of opening.
 4. The carburetor for a two-stroke engine accordingto claim 2, wherein the first cam face is formed so that the choke valvelever causes the interlocking lever to stop at a position at which thesecond cam face does not make contact with the air valve lever betweenthe fully closed position of the choke valve and a positioncorresponding to a certain degree of opening.
 5. The carburetor for atwo-stroke engine according to claim 1, wherein the throttle valve stemfixedly supports a throttle valve lever and rotatably supports theinterlocking lever, and a return spring for urging the throttle valvewith a valve-closing force is provided so as to be latched at both endsto the throttle valve lever and the interlocking lever.
 6. Thecarburetor for a two-stroke engine according to claim 2, wherein thethrottle valve stem fixedly supports a throttle valve lever androtatably supports the interlocking lever, and a return spring forurging the throttle valve with a valve-closing force is provided so asto be latched at both ends to the throttle valve lever and theinterlocking lever.
 7. The carburetor for a two-stroke engine accordingto claim 3, wherein the throttle valve stem fixedly supports a throttlevalve lever and rotatably supports the interlocking lever, and a returnspring for urging the throttle valve with a valve-closing force isprovided so as to be latched at both ends to the throttle valve leverand the interlocking lever.
 8. A carburetor for a two-stroke enginehaving an air intake passage that accommodates a throttle valve and achoke valve and feeds an air/fuel mixture to the engine, and an airchannel that accommodates an air valve and feeds scavenger air to theengine, comprising: a return spring fixedly mounted to a throttle valvestem to provide valve-closing force for urging the throttle valve and aninterlocking lever having a contact face and a cam face; a valve-openingspring fixedly mounted on the choke valve stem to provide avalve-opening force for urging a choke valve and the choke valve leverin contact with the contact face; and a valve-closing spring fixedlymounted on an air valve stem to provide a valve-closing force for urgingthe air valve and the air valve lever in contact with the cam face,wherein the choke valve lever is placed in the region beyond the turningof the interlocking lever in a state in which the choke valve is open,but is brought into contact with the contact face and limits therotation of the interlocking lever in a position at or below theposition in which the cam face is kept in contact with the air valvelever, and wherein the valve-closing spring keeps the air valve in aclosed state when the choke valve is in a closed state, and wherein theinterlocking lever is configured so that when the limitation imposed bythe choke valve lever is released, the cam face makes contact with theair valve lever at or above a certain degree of opening of the throttlevalve to cause the air valve to open in accordance with the opening ofthe throttle valve.
 9. The carburetor for a two-stroke engine accordingto claim 8, wherein the contact face is formed so that contact is madewith the choke valve lever between the fully closed position of thechoke valve and a position slightly open from this state, and contact isnot made at positions opened to a greater extent.
 10. A carburetorcomprising an air intake passage, a throttle valve located within theair intake passage, the throttle valve being mounted on a throttle valvestem a choke valve located within the air intake passage, the chokevalve being mounted on a choke valve stem, a choke valve lever coupledto the choke valve stem, an air channel, an air valve located within theair channel, the air valve being mounted on an air valve stem, an airvalve lever coupled to the air valve stem, and an interlocking leverrotatably mounted on a throttle valve stem and operably couplable to thechoke valve lever and air valve lever, the interlocking lever beingrestrainable from following the opening rotation of the throttle valve,wherein the interlocking lever includes first and second cam surfaces,and wherein the air valve lever contacts the second cam face.
 11. Thecarburetor of claim 10 further comprising a valve-opening spring fixedlymounted on the choke valve stem to provide a valve-opening force forurging the choke valve open.
 12. The carburetor of claim 10, wherein thechoke valve lever contacts the first cam face.
 13. The carburetor ofclaim 10 further comprising a valve-closing spring fixedly mounted onthe air valve stem to provide a valve-closing force for urging the airvalve closed.
 14. The carburetor of claim 10 wherein the choke valvelever is rotatable to a region beyond the turning of the interlockinglever in a state in which the choke valve is open.
 15. The carburetor ofclaim 10 wherein the choke valve lever is rotatable to contact the firstcam face and restrain the interlocking lever at a position in which thesecond cam face does not make contact with the air valve lever.
 16. Thecarburetor of claim 15 wherein the valve-closing spring brings the airvalve into a closed state when the choke valve is in a closed state. 17.The carburetor of claim 10, wherein the interlocking lever is set in aposition in which the air valve is held in a closed state by the chokevalve lever when the choke valve is closed, and the throttle valve aloneis allowed to be fully open.
 18. The carburetor of claim 10 wherein thefirst cam face is formed to contact the choke valve lever and stop theinterlocking lever at a position at which the second cam face does notmake contact with the air valve lever between the fully closed positionof the choke valve and a position corresponding to a certain degree ofopening.
 19. The carburetor of claim 10, wherein the throttle valve stemfixedly supports a throttle valve lever and rotatably supports theinterlocking lever, and a return spring for urging the throttle valvewith a valve-closing force is provided so as to be latched at both endsto the throttle valve lever and the interlocking lever.
 20. A carburetorcomprising an air intake passage, a throttle valve located within theair intake passage, the throttle valve being mounted on a throttle valvestem a choke valve located within the air intake passage, the chokevalve being mounted on a choke valve stem, a choke valve lever coupledto the choke valve stem, an air channel, an air valve located within theair channel, the air valve being mounted on an air valve stem, an airvalve lever coupled to the air valve stem, and an interlocking leverrotatably mounted on a throttle valve stem and operably couplable to thechoke valve lever and air valve lever, the interlocking lever beingrestrainable from following the opening rotation of the throttle valve,wherein the interlocking lever includes first and second cam surfaces,and wherein the choke valve lever is rotatable to contact the first camface and restrain the interlocking lever at a position in which thesecond cam face does not make contact with the air valve lever, andwherein the interlocking lever, when not restrained by the choke valvelever, is operably couplable with the air valve lever wherein the secondcam face makes contact with the air valve lever at or beyond a certaindegree of opening of the throttle valve to open the air valve.